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gdb: safety checks in skip_prologue_using_sal

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While working on the previous patch I reverted this commit:

  commit e86e87f77f
  Date:   Tue Nov 28 16:23:32 2006 +0000

          * symtab.c (find_pc_sect_line): Do not return a line before
            the start of a symtab.

When I re-ran the testsuite I saw some GDB crashes in the tests:

  gdb.dwarf2/dw2-line-number-zero.exp
  gdb.dwarf2/dw2-lines.exp
  gdb.dwarf2/dw2-vendor-extended-opcode.exp

GDB was reading beyond the end of an array in the function
skip_prologue_using_sal.

Now, without the above commit reverted I don't believe that this
should ever happen.  Reverting the above commit effectively breaks
GDB's symtab_and_line lookup, we try to find a result for an address,
and return the wrong symtab and line-table.  In
skip_prologue_using_sal we then walk the line table looking for an
appropriate entry, except we never find one, and GDB just keeps going,
wandering off the end of the array.

However, I think adding extra protection to prevent walking off the
end of the array is pretty cheap, and if something does go wrong in
the future then this should prevent a random crash.

Obviously, I have no reproducer for this, as I said, I don't think
this should impact GDB at all, this is just adding a little extra
caution.

Reviewed-By: Tom Tromey <tom@tromey.com>
This commit is contained in:
Andrew Burgess
2023-05-17 15:37:15 +01:00
parent ef56b00650
commit e84060b489
1 changed files with 5 additions and 3 deletions
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8
gdb/symtab.c
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@@ -3953,15 +3953,17 @@ skip_prologue_using_sal (struct gdbarch *gdbarch, CORE_ADDR func_addr)
struct objfile *objfile
= prologue_sal.symtab->compunit ()->objfile ();
const linetable *linetable = prologue_sal.symtab->linetable ();
gdb_assert (linetable->nitems > 0);
int idx = 0;
/* Skip any earlier lines, and any end-of-sequence marker
from a previous function. */
while (linetable->item[idx].pc (objfile) != prologue_sal.pc
|| linetable->item[idx].line == 0)
while (idx + 1 < linetable->nitems
&& (linetable->item[idx].pc (objfile) != prologue_sal.pc
|| linetable->item[idx].line == 0))
idx++;
if (idx+1 < linetable->nitems
if (idx + 1 < linetable->nitems
&& linetable->item[idx+1].line != 0
&& linetable->item[idx+1].pc (objfile) == start_pc)
return start_pc;